1. Field of the Invention
The present invention is directed to a method for automatically detecting the three-dimensional position of a medical examination instrument introduced into a body region, particularly a catheter introduced into a vessel, using a device for registering radiation images having at least one C-arm system having a C-arm with a radiation source and a radiation receiver.
2. Description of the Prior Art
To allow a physician who, for example, sets a catheter to push it into the desired target region, it is necessary that the physician receive information about the respective position or, attitude of the catheter during the displacement. The physician is basically interested only in the position of the catheter tip, whose position and alignment define the further course of motion. Conventionally, the physician has received the relevant information on the basis of transillumination images of the examination region registered with an x-ray system. Usually, transillumination images are continuously registered from two different directions, with two image planes residing at an angle relative to one another. These are presented to the physician side-by-side at a common monitor or at two side-by-side monitors. On the basis of these two images, whose image planes are usually perpendicular to one another, the physician can identify the position of the catheter in the vessel and recognize how the catheter moves in space. A disadvantage, however, is that the physician must simultaneously look at two monitors or, two images in order to obtain the required information. Another disadvantage is that the two images are merely projection images, i.e., all body parts in the projection direction are superimposed on one another. As a result, it is complicated for the physician to recognize the actually established three-dimensionally geometry on the basis of these two two-dimensional projection images, particularly when the vessel branches in an extremely irregular way.
German OS 199 19 907 discloses a method for catheter navigation in three-dimensional vessel tree exposures, particularly for intra-cranial application. A position acquisition system is utilized for acquiring the catheter position, this being positioned in the tip of the catheter and a number of markers situated at the patient and transmission coils located externally relative to the patient. The markers situated at the patient serve the purpose of defining a patient coordinate system wherein the catheter position in this coordinate is identified using the transmission coils and the position acquisition system in the catheter tip. The actual vessel tree is registered in an image coordinate system; two different coordinate systems are thus utilized therein, these being registered relative to one another using transformation matrices. For registration, there is the possibility of making use of two-dimensional projection images of the vessel tree that were pre-operatively registered and already exist, the markers serving the purpose of registration being acquired therein, with the markers being projected back onto the imaged object and brought into relationship with the marker coordinates in the patient coordinate system using the projection matrices that exist for the respective two-dimensional projection images, these projection matrices having been determined for the reconstruction of the three-dimensional volume set.
Further, German PS 198 43 408 provides a method for reproduction of x-ray images with the assistance of an x-ray device when positioning a catheter introduced into a vessel. In this method, first, a number of two-dimensional individual images are registered from different directions and a three-dimensional image dataset is subsequently generated; a three-dimensional image is determined based thereon and reproduced, this showing the vessel. Thereafter, a second two-dimensional individual image of the vessel with introduced catheter is generated from a specific registration direction. Subsequently, a two-dimensional mask image is generated from the three-dimensional image dataset, the registration direction of the mask image corresponding as best as possible to the exposure direction of said two-dimensional individual image. Subsequently, the generated mask image is combined with the registered, second two-dimensional individual image to form a combination image of the vessel with catheter introduced therein. This combination image is subsequently output in order to be able to identify the catheter position in the vessel on the basis thereof.